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March 2nd, 2012

Donut sweat the little stuff: Nanostructured ceramics and safety, processing, applications

Published on March 2nd, 2012 | By: Eileen De Guire

Is there a recommended daily allowance for nanoparticles? If so, powdered donuts are a reliable source. Credit: kilrothi; Wikipedia; Creative Commons license.

How do you like your nanopowders? I like mine on a leisurely Sunday morning, with a cup of coffee and the Sunday paper. That’s because some of the delicious whiteness of a powdered donut is actually nanosize titania. (If only the “substrates” had a less macroscopic affect on body mass index!)

I did not know about the nano-titania and donut connection until I talked to a favorite college student, who told me about a chemistry lab that involved “extracting” the nanopowdered TiO2 from donuts and getting anthrocyanin from blueberries to make a rudimentary solar cell. (I was surprised to find out that I’m late to this knowledge. Wired magazine has a how-to video and a physics professor in South Carolina is all over it like white-on-donuts. It is proof, too, that one can learn a lot by talking to one’s children.)

Applications for these puny particles with their unique properties seem to be without limit. But there are also concerns about safety regarding processing, handling and use. And rightly so — nobody wants another “asbestos” or “thalidomide” — but as a report issued late last year says, “The size label ‘nano‘ does not also immediately mean ‘toxic,’ so it does not represent an intrinsic hazard characteristic” (authors’ emphasis).

The report (pdf) out of Germany, “10 Years of Research: Risk Assessment, Human and Environmental Toxicology of Nanomaterials,” is a status paper published by the DECHMA/VCI working group, “Responsible Production and Use of Nanomaterials.” The working group is comprised of mostly German and Swiss chemists, so the emphasis is on German risk assessment projects, but encompasses some European research projects, too.

Also, in January we told you about a report by the National Academies calling for a cohesive plan for research safety issues regarding nanotechnology and also a Danish database concept for cataloging and evaluating risks. Readers may recall our earlier story about the safety of sunscreens with nanosize ZnO particles, too.

One of the theme areas of the Fourth International Congress on Ceramics (July 15-19, Chicago, Ill.) is Nanostructured Ceramics. At present, six invited talks are scheduled—including the conference’s keynote speech by Maxine Savitz, “Materials: An Enabler”—and over two dozen poster sessions.

The talks and posters address processing, properties and applications of nanoceramics, and many will touch on health and safety issues, either directly or indirectly.

Debra Kaiser of NIST, for example, is giving an invited talk, “Environmental, Health and Safety Assessment of Engineered Nanomaterials.” The abstract explains:

The promise of nanotechnologies and the ensuring economic and societal benefits may never be fully realized due to unknown risks of engineered nanomaterials (ENMs)-materials with at least one dimension in the 1 to 100 nm range that are purposefully produced-and ENM-enabled products throughout all stages of their life cycles. ENMs pose risks to the environment (E) and the health (H) and safety (S) of workers, consumers, and the public. The National Nanotechnology Initiative recently released a document entitled 2011 Environmental Health and Safety Research Strategy, which is the product of an interagency effort on research needs to enable assessment of the EHS risks of ENMs. NIST is the lead agency on the development of a Nanomaterial Measurement Infrastructure, a suite of tools that enable accurate, precise, and reproducible measurements of nanomaterial properties. The needs and status of the tools-protocols, standards (reference materials and documentary standards), instruments, models, and data-will be described, with a particular emphasis on the importance of ENM standards.

Kathleen Eggleson of the University of Notre Dame will talk about mesoporous silica nanopowders, and the balance between health-enhancement and toxicology of nanoparticles in her invited talk, “Mesoporous Silica Nanoparticles and the Quest to Deliver Biomedical Benefits.”

Mesoporous silica nanoparticles have emerged as nanobiotechnology standouts, particularly as drug delivery vehicles. MSNs are advantageous due to capacities to: transport large molecular payloads within their pores, enhance solubility of hydrophobic pharmaceuticals, target drug release, and control release kinetics through multiple mechanisms. MSNs have demonstrated potential as doxorubicin vehicles toward overcoming multiple drug resistance of tumors. Recent studies have pointed to MSN pore structure as critical in cell-nanoparticle interactions. When MSNs were incubated with phosphate-buffered saline, loss of pore integrity was associated with increased hemolytic activity. While some have found that elicitation of pro-inflammatory and apoptotic responses are significantly reduced with MSNs compared with colloidal silica nanoparticles equivalent in shape and size, others conclude that their toxicological qualities are roughly equivalent. This talk will explore the latest research regarding MSNs with respect to biomedical outcomes.

Other talks and posters do not focus directly on EHS issues, but the more we understand about processing nanomaterials, the better we will be able handle them on a commercial-scale. Jon Binner of Loughborough University (UK) will present work in his poster, “Processing of Nanostructured Ceramics,” which is on the verge of commercialization.

Microstructures of nano and conventional, commercial yttria partially, or fully, stabilized zirconia. Credit: Binner

Microstructures of nano and conventional, commercial yttria partially, or fully, stabilized zirconia. Credit: Binner.

The ability to produce genuinely nanostructured ceramics with mean grain sizes <100 nm has been achieved for yttria partially stabilized zirconia and is being developed for alumina, barium titanate, zirconia toughened alumina and yttrium aluminum garnet under a range of different Government and industrially-funded projects. Prototype components have already been produced and characterized for the YSZ, BT and ZTA and the work on YSZ is expected to be licensed to an industrial company before Easter 2012 for subsequent commercialization. This presentation will highlight the key steps and demonstrate the achievements. Opportunities to fund research into the processing of other nanostructured ceramics will be presented.

Jow-Lay Huang of National Cheng Kung University will also focus on processing in his invited talk, “Spark plasma sintering of β-Si3N4 nanoceramic and its indentation behavior.”

The elastoplastic deformation mechanisms is different for the two ceramics during intentation tests.

The elastoplastic deformation mechanisms are different for the two ceramics during indentation tests. Credit: Huang.

A successful fabrication of high wearing parts based on Si3N4 polycrystal requires an understanding of several important properties of this material, of which the mechanical deformation behavior is the most significant. Investigating the processes controlling the contact deformation and micro-fracturing behavior of Si3N4 based materials are thus of physical interest and technological importance, and the mechanical and tribological properties can be much improved. A commercial available nanosized β-Si3N4 doped with uniformly dispersed sintering additives has been used and consolidated by spark plasma sintering. The use of slow and fast heating rate yield nanosized and large, elongated β-Si3N4 based grains, respectively. During SPS process, temperature differences between inner and outer graphite mold and overshooting, which are related to power input and arrangement of graphite mold, are taken into consideration. The effects of microstructure on the indentation responses and micro-damaged evolution of spark-plasma-sintered β-Si3N4 based ceramics has been evaluated through depth-sensing-indentation tests. It was found that the nanoceramic and its coarse-grained counterpart exhibit similar elastoplastic behavior in their indentation responses. However, the increased hardness and ratio of elastic work to total work done in the nanoceramic suggest that the resistance to plastic deformation is greater than that in the coarser-grained one. The microcracking behavior within the indented materials is also evaluated and proposed in the present study.

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